1. Field of the Invention
The present invention relates to a sheet feeding unit which is used in an image forming apparatus such as a copying machine, a laser beam printer, and a facsimile.
2. Description of Related Art
In the image forming apparatus such as the copying machine and the laser beam printer, a plurality of sheet trays are arranged in a sheet feeding portion, and each of sheets having the different sizes and types is stored in each sheet tray. The corresponding sheet stored in the sheet tray is fed according to the size of an original, magnification and reduction rates, and the like. In addition to the sheet trays in which fixed type of sheet are stored, generally a manual sheet feed tray is further arranged in a side portion of the apparatus main body in the image forming apparatus. Namely, a mechanism which can feed a small number of special sheets, a special type of sheet which cannot be stored in the sheet tray like an OHP sheet, a thick sheet such as a post card, and the like is provided in the image forming apparatus.
For example, as disclosed in Japanese Patent Application Laid-Open No. 2001-010160, the manual sheet feed tray includes a sheet feeding device which generally separates and feeds the plurality of sheets stacked on the manual sheet feed tray one by one.
Recently, in the image forming apparatus, there is a demand that the common mechanism is unitized and commonly used for the different image forming apparatuses. When the similar mechanism is formed as a common unit, there are advantages in reduction of production cost, reuse property of the common unit, supply of maintenance parts, and the like.
Because the manual sheet feed tray is common in the mechanism in which the small number of special sheet is fed to the apparatus, that the manual sheet feed tray is unitized as a sheet feeding unit and commonly used among the different image forming apparatuses is beginning to become widespread.
However, in the image forming apparatus including a manual sheet feed tray 101, there are two types of sheet conveyance paths. Namely, in the sheet conveyance path immediately after a sheet conveyance path through which the sheet is conveyed from the manual sheet feed tray 101 to an apparatus main body (hereinafter referred to as manual sheet feed path 102) is merged into a sheet conveyance path on the side of the apparatus main body (hereinafter referred to as main body path), the case in which the sheet conveyance path is parallel to the manual sheet feed path 102 as shown in FIG. 16A hereinafter referred to as parallel path 104) and the case in which the sheet conveyance path is perpendicular to the manual sheet feed path 102 as shown in FIG. 16B (hereinafter referred to as vertical pass 105) exist.
For example, when the manual sheet feed tray 101 is produced according to the parallel path 104, a sheet separation roller pair 106 is arranged so that a direction of a nip line of the sheet separation roller pair 106 becomes parallel to the parallel path 104 (see FIG. 16A). When the manual sheet feed tray 101 is unitized and used as a sheet feeding unit 100 to the image forming apparatus with the vertical path 105, an angle between the vertical path 105 and the direction of the nip line of the sheet separation roller pair 106 becomes substantially 90° (see FIG. 16C). Therefore, when the sheet is conveyed so that the sheet is transferred from the manual sheet feed path 102 to the vertical path 105, the sheet is conveyed while largely curved by the conveyance path. Namely, the fed sheet is largely bent in a merging portion of the manual sheet feed path 102 and the vertical path 105. Because sometimes the manual sheet feed tray 101 feeds the special sheet, when the sheet is largely bent in feeding the thick sheet having high rigidity, the sheet is largely damaged, or conveyance failure is generated due to the high rigidity of the sheet.
When the manual sheet feed tray 101 is produced according to the vertical path 105, the sheet separation roller pair 106 is arranged so that the direction of the nip line of the sheet separation roller pair 106 becomes oblique with respect to the vertical path 105 (see FIG. 16B). When the manual sheet feed tray 101 produced according to the vertical path 105 is unitized and used as a sheet feeding unit 1000 to the image forming apparatus with the parallel path 104, it is necessary that the manual sheet feed path 102 is largely bent to merge the manual sheet feed path 102 into the parallel path 104 (see FIG. 16D). Therefore, as with the above-described case, when the thick sheet having high rigidity is fed from the manual sheet feed tray, the sheet is largely damaged.